The spell system is honestly really cool (who doesn't like magic?). As Extra Jos said, it reaaally needs some particle effects, which would be pretty fast to make since you work in unity.
The game seems to have some pretty game-breaking bugs tho (expected in this timeframe), for example. spells turn invisible and don't do anything, but mana still runs. the explosion spell also works maybe like 10% of times :D but nothing a small restart doesn't fix.
Other than that really cool game! I could definitely see a bigger polished version of the spell-book system made in the future, so good job on that!.